The following correction was printed in the Guardian's Corrections and clarifications column, Tuesday 1 September 2009

In the article below we called Abdul Rashid Dostum a Tajik leader: he is Uzbek.

During the last Afghan elections, a UN official outside a polling booth grabbed a voter's blue-stained finger and raised it before the cameras. "Look," he said ecstatically. "This is what it's all about."

No, it isn't. Even in its present belligerent stance, the western world does not go about bombing and killing people just so they can vote. The Afghan war and occupation were about punishing the Taliban for harbouring Osama bin Laden and to prevent them ever doing it again. The punishment was delivered. The prevention was, and remains, ill-conceived and elusive.

No believer in self-government can decry the vote. It remains the essential ritual of democratic grace. Tomorrow's election reflects the aspirations of millions of Afghans. It is an advance on the earlier Islamist fundamentalism and offers voters both a choice of leader and an opportunity, albeit at great personal risk, to share in the national polity.

Even the likely triumph of Hamid Karzai as president does not invalidate this cause. For a nation as poor as Afghanistan to tolerate a contested election that embraces Ashraf Ghani, the darling of the Kabul NGOs, is an achievement, even if impossible without the presence of a huge foreign army. Any distraction from the politics of death, destruction and corruption must be welcome.

Voting is one thing, elections another. tomorrow's election will make no difference to the ramshackle structure of government in what, nearly eight years after the Nato invasion, is a wholly dysfunctional state. While western diplomats are right to protest that no one should expect a lily-white poll in such a country, the awesome scale of electoral pollution should make even nation-building's most ardent defenders pause to think.

Reports are rife of vote selling, ballot rigging and general chicanery. Karzai's running mate is the dubious warlord Mohammad Qasim Fahim, and he has allowed back the brutal Tajik leader Abdul Rashid Dostum from well-deserved exile. Low turnout in the Taliban-dominated centre and south may well tilt Kabul towards the non-Pashtun north, distorting national politics.

As Malalai Joya, a brave young member of parliament, said recently on a tour in Britain, Afghanistan is a kleptocracy rather than a functioning democracy. Her assertion, that people (especially women) are no better off than under the Taliban, is not for outsiders to contest.

This will further enhance emerging local Taliban leaders as defenders of the Pashtuns against the Karzai regime. With violence increasing, Kabul is readying itself for what may again be its fate, sooner rather than later, as a besieged city awash in old divisions and conflicts, which the west is powerless to avert.

Britain has no real dog in this fight. Ever more bombs explode across British-occupied Helmand, and mayhem rules the day. There is no grimmer testament to the failure of three years of "hearts and minds" than that only three of Helmand's 13 electoral districts are reportedly safe for election monitors to attend. Barely half the province's voters can be assured an open polling station. The Taliban is everywhere and the idea, much touted by British ministers, that this is "ridding the streets of Britain of the terrorist menace" is absurd.

Even if the Taliban cared to disrupt the streets of Britain, which they do not, the Afghan operation must constitute the biggest incitement to global mischief ever invented. As the Guardian's Ghaith Abdul-Ahad has been writing this week, a nation that under the Taliban was introverted and passive (save for its unwitting role in 9/11 as host to Bin Laden) is now a magnet for international killers and fanatics. British policy, whatever it was, simply has not worked. It has failed. No amount of platitudes from London or Washington can alter that.

This election should be a moment of truth for liberal interventionists everywhere. To cruise the world instigating elections at the point of a gun may have conferred neocon street cred on George Bush and Tony Blair. It has met its nemesis in the partition of Yugoslavia, the reversion of Iraq to feuding religious rivalry, and the chaos of Afghanistan. Other theatres of this missionary zeal – Pakistan, Palestine, Sudan and, in a different sense, Iran and Burma – are not glowing advertisements for the policy. Who knows where it will next bless with democracy at the blast from a drone?

Interventionists argue that the ideology of global philanthropy is naturally drawn to tough cases. Christianity scored its most remarkable successes in the pagan wastes of Africa and Latin America, in Borneo and the putrid slums of the Philippines. Liberal intervention may be ambitious, in leaping from anarchy to democracy without an intervening imperialism, but that is still a noble goal. The Afghan's blue finger may soon be cut off by the Taliban, but at least the photo-opportunity stands to Nato's credit.

I do not see why. Afghanistan has become a lucrative melting pot of idealistic NGOs, underemployed diplomats and hi-tech weapons salesmen. Tomorrow's election stands alongside opium eradication and gender awareness courses in the long history of "telescopic philanthropy", as satirised by Dickens in Mrs Jellyby. Her children could starve while she devoted herself, "until something else attracted her, to the subject of Africa, the general cultivation of the coffee berry and the natives". She is reincarnated in Douglas Alexander, Britain's development secretary, and his "immense challenge of Afghanistan".

In retrospect, Donald Rumsfeld is a better guide to Afghan policy. His original intention to punish the Taliban by backing the northern tribes, and getting out before being sucked into nation-building, was in retrospect prudent and pragmatic. Don't get involved, he warned. Let Afghans arrange their future, whatever it may be.

Had such a policy been pursued after 2001, the Taliban would probably have returned to power in some new alliance, possibly under the quiet influence of their old Soviet-era allies, the American CIA – with whom they were re-establishing links prior to 9/11. Were Nato troops not present, magnetising and revitalising al-Qaida, Pakistan could have refashioned a new Afghan policy that better accorded with the west's security interests. By now, the country would surely have settled into a new isolation from the world.

I imagine this will eventually come to pass, but only after a decade of chaos instigated by the present intervention. As in Vietnam, there will first have to be a battle in Washington and London, between brave realists and fake patriots. This is now joined. Once gung-ho publications (such as the Times and Economist) are asking tough questions, even if they dare not offer answers. Ministers are sounding ever more panic-stricken. Generals are forewarning of retreat by pleading for sympathy and resources.

A bombastic crusade has mutated into a long, hard slog, and now into a state of despair. The daily ritual of soldiers' deaths should be acceptable to a nation at war. But there comes a point in the rhetoric of heroism when the pointlessness of it all bursts the shackles of jingoism. Surely an election, the ultimate moment of political realism, is the time to stop mouthing insincerities and call a mistake a mistake.

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